Wireless communication systems are widely deployed to provide various communication services such as telephony, video, data, messaging, broadcasts, and so on. These systems commonly employ an access network capable of connecting multiple access terminals to a wide area network (WAN) by sharing the available network resources. The access network is generally implemented with multiple access points dispersed throughout a geographic coverage region. The geographic coverage region is generally divided into cells with an access point in each cell. The cell may be further divided into sectors. The access point generally includes one transceiver function for each sector in the cell. The transceiver function provides an air interface attachment point for access terminals in the sector.
The access network may also include one or more network functions. In a typical configuration, the network function acts as a controller for any number of transceiver functions and performs various tasks including allocating, managing and tearing down resources for the access terminals. The network function also provides an Internet Protocol (IP) layer attachment point (IAP) for the access terminals. All IP packets destined for the access terminal are sent via the IAP. The access network may have a centralized network architecture defined here as multiple network functions supporting multiple access points, i.e., each network function supporting multiple access points and each access point supported by multiple network functions, or a distributed network architecture defined here as dedicated network function for each access point, i.e., each network function supports a single access point and each access point is supported by a single network function.
In addition to providing an IP layer attachment point, the IAP may also responsible maintaining a session state for any number of access terminals. The session state for an access terminal is the state of the access network on the control path between the access terminal and the IAP that is preserved when a connection is closed. The session state includes the value of the attributes that are negotiated between the access terminal and the access network. These attributes affect the characteristics of the connection and the service received by the access terminal. By way of example, an access terminal may negotiate the quality of service (QoS) configuration for a new application and supply new filter and flow specifications to the access network indicating the QoS service requirements for the application. As another example, the access terminal may negotiate the size and type of the headers used in communication with the access network.
In some wireless communication systems, an access terminal in a given sector establishes a connection with an access point by making an access attempt on an access channel of a transceiver function serving that sector. The network function associated with the transceiver function receiving the access attempt contacts the session master for the access terminal and retrieves a copy of the access terminal's session state. The session master could be a centralized or distributed entity and may or may not be colocated with the IAP. On a successful access attempt, the access terminal is assigned air interface resources such as a MAC ID and data channels to communicate with the transceiver function serving the sector. In addition, the IAP is moved to the serving network function, or alternatively, an IP tunneling protocol is used to send IP packets between the IAP and the serving network function.
In some wireless communication systems, once the access terminal establishes a connection with an access point, it listens for other sectors and measures the signal strength of the sectors it can hear. The access terminal uses these measurements to create an active set. The active set is a set of sectors that have reserved air interface resources for the access terminal. The access terminal will continue to measure the signal strength of other sectors and may add or remove sectors from the active set as it moves around the access network. Alternatively, the access terminal can send a report of the signal strength measurements to the access network so that the access network can maintain the active set.
One function of the active set is to allow the access terminal to quickly switch between sectors and maintain service without having to make a new access attempt. This is achieved by (1) reserving air interface resources for the access terminal in each of the sectors in the active set, and (2) providing a copy of the session state from the session master to each network function serving a sector in the active set. With this approach, the handoff between the sectors can be achieved while minimizing the affect on the QoS service of active applications.
Heretofore, there has been one session state (i.e., a global session state) for an access terminal, and each network function serving a sector in the active set has been required to synchronize to that state. However, it is possible that a network function may want to change the session state temporarily without affecting the global session state maintained at the session master. By way of example, an application such as voice over IP (VoIP) may not require admission control as part of its session state profile, but a very loaded network function may want to require admission control for that application if it is started. Similarly, a network function may want to make a local admission control decision to accept an application, while not wanting to change the global session state for an access terminal to automatically accept that application for admission control on handoff.
As another example, a network function may want to locally disable or enable some features based on the capabilities of the network function. For instance, a network function may have sectors with extra capabilities such as additional antennas as compared to neighboring sectors and may want to use some advanced coding or modulation schemes such as multiple-input multiple-output (MIMO) or beam-forming when communicating with the access terminal. This network function may want to change some local attributes to enable these capabilities without updating the global session state.
Accordingly, there is a need in the art for a mechanism that enables a network function to define a local session state without affecting the global session state for the access network.